Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$7.38	12.805%	$8.325	$8.33	$8.35	$8.30
Purchase #2	$56.40	5.722%	$59.6272	$59.63	$59.65	$59.60
Purchase #3	$45.64	11.269%	$50.7832	$50.78	$50.80	$50.80
Purchase #4	$34.82	11.724%	$38.9023	$38.90	$38.90	$38.90
Purchase #5	$195.68	13.827%	$222.7367	$222.74	$222.75	$222.70
Purchase #6	$98.93	6.761%	$105.6187	$105.62	$105.60	$105.60
Purchase #7	$217.81	3.688%	$225.8428	$225.84	$225.85	$225.80
7 purchase totals =	$656.66		$711.8359	$711.84	$711.90	$711.70